P0420 -100.6% ST<FT 3

Also, gas mileage has dropped dramatically over the past 6 fill ups. 127 miles to my last fill up.

I actually just had a tune up Friday. I wont be able to check the sensors until tomorrow. I am going to reset via battery and take a ride and check the fuel trim again. My CEL went off on its own so that info was my most recent Freeze frame since my last CEL and repair. I am a very new to working on cars. When my last car threw this code and my o2 sensors were bad it would idle funny and misfire. However my ONLY indication of a problem outside of freeze frame was filling up today after 127 miles for a full tank.

Check engine light came on for about 60 miles and went of as I pulled into my dads driveway to pick up the code reader.

His is not, but I am at a friends getting it checked now. I'll post results as soon as I have them

My live codes showed no faulty o2 sensors. Front or rear. I Ran a can of sea foam thru the tank, seems to have increased my gas mileage back up to 221 a tank. On my tune up I just realized they did an oil change, visual check of hoses and fluids made sure nothing was mixing or leaking where it shouldn't be. My next culprit is ugly plugs. If I am headed the wrong direction please let me know. Even after sea foam and pcv replacement the issue it self is still existant. Now I have ruled out my o2 sensors it only makes sense to change the plugs. Idk. Any reccomendations and insight would be much appreciated. Ft3 was -89st -78.7Lt